NeilR,
Since the introduction of JAR-FCL, the logbook has no "holder's operating capacity column". Time is logged as Pilot in command, co-pilot or dual.
In this case, one pilot loggs the flight as pilot in command and the other loggs the time as co-pilot.
See the following definition of co-pilot with my emphasis;
“Co-pilot” means a pilot operating other than
as pilot-in-command, an aircraft for which more
than one pilot is required under the list of types
of aeroplanes (see Appendix 1 to JAR-FCL
1.220) or the type certification of the aircraft, or
the operational regulations under which the flight
is conducted, but excluding a pilot who is on
board the aircraft for the sole purpose of
receiving flight instruction for a licence or rating.
The operating regulations require two pilots. Two pilots must record their presence and relative roles on the flight.
Note that this does not apply to being a safety pilot for a person who holds a medical limitation. There is different guidance in JAR-FCL 1 regarding that.
Regards,
DFC